I'm assuming that you are thinking of showing them in your own home or own personal workspace, or putting them in an album to show them to others - without any commercial interests whatsoever being involved.
My answer is - who is likely to complain about it?
While that may sound a bit flippant, it is also highly relevant.
If there isn't anyone who will likely seek a legal remedy against you for what you are doing, then it isn't likely that you need worry about it.
And if you are concerned about the morality of printing the negatives I would suggest you ask yourself whether the holder of the copyright is even potentially losing anything by your doing so.
I would have a different answer if you either recognized the images as being publicly well known and/or knew of who might own the copyright.